1. Field of the Invention
This invention relates generally to optical connectors, and more particularly, to optical connectors used between high speed backplanes and electronic modules.
2. Description of the Prior Art
High speed and high bandwidth digital transmissions between the backplanes and add-on electronic modules become more and more important for many electronic systems. Fast progress in the CPU technology has made the clock rates of most system buses increase in a dramatic speed. Besides, the improvements in digital signal processing have made it possible for computers to process not only the traditional text- or number-based applications, but also sound- and image-based multimedia applications. The need for much higher digital transmission bandwidth becomes very apparent for new electronic system applications.
Fortunately, the semiconductor and board-level packaging technologies have advanced quick enough to catch up the need for higher speed and capacity. Processors which are capable of running up to several hundreds megahertz are available for quite a while. And the multi-chip module (MCM) technology which allows many silicon dies to be bonded directly to a MCM board with high density traces in between also becomes available to the market for those high speed and high bandwidth applications. But connector interfaces between backplanes and electronic modules, or between two circuit boards, seem to be difficult to catch up with the progresses made in other fields.
There are two reasons why it is difficult for today's connector technology to catch up with the progress in semiconductor or packaging technologies. First, most of the mechanical components such as pins and sockets used in today's connectors are small enough and difficult to be shrunk again. Such mechanical parts become very difficult to manufacture or use when their sizes become too small. It is already difficult enough to make the pins of a mechanical connector down to sub-millimeter range, while it is quite normal for the semiconductor or packaging technologies to cut their circuit traces down to sub-micron or mil ranges. The result is that big and bulky connectors are still used in many advanced systems while most of the electronic circuits have shrunk into small silicon dies or MCM packages.
Second, high speed and high bandwidth digital transmissions require special care in order to maintain signal integrity. To control noise, crosstalk, reflections and distortion, high performance connectors have to be engineered as transmission lines. That demands a new level of sophistication on the part of connector and interface circuit design. Besides, many advanced electronic applications such as portable computers do not provide enough spaces for big connectors to fit in. That means new connectors for such electronic systems must be able to provide higher performance and pin-density which can be fit into smaller packages. Such requirements not only make the high performance connectors very expensive, but also cost more for the related electronic engineering efforts, manufacturing equipments and processes. Traditional pin-and-socket mechanical technology seems to have a very difficult time in such high performance connector design. Besides, there is no guarantee that such technology will work when electronic transmission speed over connecter interfaces get to the gigahertz range. New approaches must be devised to solve such problems.